Struct RangeDecoder 

pub struct RangeDecoder<R: Read> { /* private fields */ }

Streaming range‐decoder for arithmetic coding.

The decoder maintains three internal registers:

• low: the low end of the current coding interval
• code: the buffered input bits read from the stream
• range: the size of the current coding interval

On each symbol decode, you first call [get_freq] to map the current code to a frequency within the total frequency range, then call [decode] to narrow the interval and consume bits as needed.

Example

use std::fs::File;
use ppmd_core::{RangeDecoder, PpmModel, PpmResult};

fn decode_stream() -> PpmResult<()> {
    let file = File::open("data.ppm")?;
    let mut decoder = RangeDecoder::new(file)?;
    let mut model = PpmModel::new(5)?;
    let mut history = Vec::new();
    let mut out_byte = [0u8; 1];

    // Repeatedly call `decode_symbol` until end of stream
    while model.decode_symbol(&mut decoder, &mut history, &mut out_byte).is_ok() {
        print!("{}", out_byte[0] as char);
    }
    Ok(())
}

Implementations

impl<R: Read> RangeDecoder<R>

pub fn new(reader: R) -> PpmResult<Self>

Initialize a new RangeDecoder by reading the first 4 bytes from reader into the internal code register.

The range decoder uses these first 32 bits as its starting buffer. Subsequent calls to [get_freq] and [decode] will consume more bytes from reader as needed to renormalize the interval.

Errors

Returns PpmError::IoError if reading the initial 4-byte code prefix fails.